Mixed refrigerant system



Dec 27 1 av ASHLEY 2 MIXED REFRIGE STEM Filed Apri 9' 45 FlG.l

CONDENSER REFRKSERANT CONDENSER OOOLANT uemum To as OOOLED 1/ EVAPORATORREFR\GERANT INVENTOR.

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EMPER Patented Dee. 27, 1949 MIXED REFRIGERANT SYSTEM I Carlyle M.Ashley, Fayetteville, N. Y., assiznor to 7 Carrier Corporation,Syracuse, N. Y., a corporation of Delaware Application April 9, 1945,Serial No. 587,385

6 Claims. (Cl. 62-115) This invention relates to refrigeration, and moreparticularly to the use in a refrigeration cycle of a plurality ofrefrigerants having different boiling points which are miscible witheach other in liquid form.

Prior to the instant invention, refrigeration systems have usually beencharged with a single refrigerant having a relatively high boilingpoint, or a single refrigerant having a relatively low boiling point andthe heat exchangers incore porated in such systems, (condensers andevaporators) have been designed to meet the requirements of therefrigerant used.

Some prior refrigeration systems have been designed to employ tworefrigerants having different boiling points and so arranged that one ofthe refrigerants evaporates in one evaporator while the otherrefrigerant evaporates in a separate evaporator so that the twoevaporators may serve two spaces at two different temperature levels.

It is an object of the invention to provide a novel refrigeration systemutilizing a plurality of miscible volatile refrigerants having differentboiling points in such manner that the heat exchange surfacesincorporated in the system are utilized more efficiently.

It is a further object of the invention to provide a novel refrigerationsystem including an evaporator adapted to utilize a plurality ofmiscible refrigerants having different boiling points whereby the heatexchange surface of the evaporator will be utilized more efficiently.

It is a further object of the invention to pro vide a novelrefrigeration system wherein a plurality of miscible refrigerants ofdifferent boiling points will be efficiently condensed withsubstantially maximum effective use of the heat exchange surface of thecondenser forming part of the system.

In general, applicant teaches the effective use in a system ofrefrigeration of a plurality of miscible refrigerants having differentboiling points (vapor pressures), wherein the refrigerant vapor and therefrigerant liquid flow together in parallel relationship. Thus, incondensing such a refrigerant mixture, initial condensation, whichoccurs at a relatively high temperature, will result in formation ofcondensate rich in the component of higher boiling point and poor in thecomponent of lower boiling point. As the condensing action proceeds withthe coolant in counterfiow or cross-flow relationship providingprogressively lower temperatures, successively smaller increments of thecomponent of higher boiling point and progressively larger increments ofthe component of lower boiling point will be produced in the condensate.Finally, with condensation at the minimum temperature, a maximumconcentration of the component of lower boiling point will be found inthe condensate with the maximum concentration of the component of higherboiling point theretofore largely condensed at higher temperatures.

Such a process involves no irreversible loss of thermal head since thevapor and the corresponding liquid phase are at each point in contact.There is a progressive interchange of the two components between thevapor and liquid phase which proceeds apace with the condensing actionto maintain the vapor and liquid in equilibrium.

The process is reversible. In the evaporator,

the first vapor produced is rich in the components of lower boilingpoint and as the refrigerant mixture progresses through the evaporator,with the medium to be cooled progressively being higher in temperature,less of the component of lower boiling point and more of the componentof higher boiling point will vaporize. Proximate the discharge end ofthe evaporator, the component of lower boiling point will have beenlargely vaporized and the vaporization of the component of higherboiling point, in maximum volume, will take place. The liquid at eachpoint is in equilibrium with the vapor, (the component of low boilingpoint having a high vapor pressure and high volatility with thecomponent of high boiling point having a low vapor pressure and lowvolatility).- The nature and advantages of the invention will beapparent from the following description taken in conjunction with theaccompanying drawing, wherein:

Fig. 1 is a schematic view of a refrigeration system in accordance withthe invention; and

Fig. 2 is a chart of temperatures plotted against a "travel through theinterchanger of condenser refrigerant, condenser coolant, medium to becooled, and evaporator refrigerant.

Referring to the drawings, the charge, comprising a plurality ofmiscible refrigerants having different boiling points, as for exampletwo refrigerants of the halogen series CClzFz and CHClF'2 is compressedby thecompressor l0 and passed upwardly to the top coil of the"condenser 3 miscible components passes in the direction of the arrowswithin the conduit or feed line l3. through the expansion valve l4,controlled by the thermal bulb l5; which is in contact with thedischarge line I! leading from the evaporator l6, and thence into thesuction l8 and back to compressor I0. The solid line arrows l9 designateone of the components of the multiple refrigerant which component has aknown boiling point at a given pressure. The dotted line arrowdesignates a second component of the multiple refrigerant, whichcomponent has a different boiling point at the same given pressure. Thecomponents l9 and 20 are miscible with each other. The componentrefrigerants which are used in the refrigeration system, may be selectedfrom refrigerants which are known to be miscible with each other andknown to have different boiling points at a given pressure. Theinvention is not limited to any two or more refrigerants. While theschematic drawing discloses the use of two refrigerants, it is to beunderstood that it is contemplated that more than two refrigerants maybe used.

It is contemplated, in accordance with the invention, that the coolantfor the condenser H will in general be passed in counterflow relation tothe passage of the multiple refrigerant through the condenser II. Thecoolant may be a gas, such as air, or a liquid, such as water. In thecase of water, for example, the flow of condenser coolant may be througha tube I la of larger diameter and concentric with the condenser tube."In the case of air cooling, a fan will be employed at one end of acasing in which the condenser is housed. In either case, as is wellknown, substantially a. counter-flow or, in some cases, a cross-flowrelationship will be provided to secure most effective heat exchange.

The medium to be refrigerated or cooled will also be passedsubstantially in counterflow or, in some cases, in crossflowrelationship to the flow of refrigerant through evaporator I in the samegeneral manner as that describedin connection with the coolant for thecondenser. That is, the medium to be refrigerated may be passed in truecounterflow relationship to the passage of the refrigerant through'theevaporator tubes, for example, in the case of water, through a tube lGaof larger diameter, or it may be passed generally in counterflowrelationship to the evaporator by passing the medium to be cooledupwardly and transversely of the tubes of the evaporator which carry therefrigerant generally downwardly therethrough.

Bearin in mind that a counterflow relationship exists between thecondenser and its coolant, the relatively low temperature coolant willfirst contact the bottom tube of the condenser which contains a.multiple refrigerafnt also of relatively low temperature. When thecoolant reaches the top tube of the condenser, it will .be relativelywarm and, correspondingly, the multiple refrigerant within the top tubewill be in gaseous form.

As the multiple refrigerant passes downwardly thru the condenser, itbegins to liquefy and the liquid so formed is rich in the refrigerantcompo= nent of higher boiling point (or condensing point). As themultiple refrigerant continues further downwardly through the condenserand contacts ascending coolant of relatively low temperature, greateramounts of the refrigerant component of lower boiling point (orcondensing point) will liquefy until the lowest tube of the condenser isreached when all of the refrigerant 4 component of lower boiling pointis condensed. The various refrigerant components liquefy togetherthroughout the process and-the liquid at any time during passage of therefrigerant through the condenser 'difl'ers only in the concentration ofthe various components, that is, being relatively weak or rich in anygiven component. The mean temperatures of the multiple refrigerantwithin the condenser, as well as the temperatures of the condensercoolant as it travels through the condenser, correspond to the twoparallel sloping lines at the top of the chart in Fig. 2. As the twolines tend to be parallel when a proper choice of the components of themultiple refrigerant is made in relation to temperature difference, itwill be apparent that there is a substantially constant temperaturedifferential between the condensing refrigerants and the coolantindicating that the condenser surface is greater proportion than thecomponent refrisbeing utilized at even efliciency and with optimumeffective use of the surface throughout its length. If a singlerefrigerant were utilized in the same condenser with the samecounterflow relationship, the refrigerant would condense at asubstantially constant temperature and the line marked.condenserrefrigerant on the chart in Fig. 2 would be horizontal as long as somesubstantial amount of refrigerant remained to be condensed; and hencethe curve would not be parallel to the line corresponding to thecondenser coolant temperature. Further, the condenser coolanttemperature would tend to slope upwardly more sharply so that thetemperature differential between the coolant and the refrigerant wouldbe greater at the bottom of the condenser than at the top. Accordingly,when a single refrigerant is used, the temperature differential cannotbe the same throughout the length of the condenser and, accordingly,only a portion or small fraction of the condenser can be operated athigh efficiency insofar as heat exchange is concerned while theremainder of the condenser surface is operated at progressivelydecreasing efficiency.

The principle of operation described in connection with the condenser issimilarly true in connection with the operation of the evaporator l6. Asthe medium to be cooled is passed in counterflow relationship with themultiple refrigerant, the relatively warm medium first contacts thelowest tube of the evaporator which is relatively warm and when themedium reaches the top tube of the evaporator, it is relatively cool asis also the refrigerant in the top tube of the evaporator. As therefrigerant passes downwardly through the tubes of the evaporator, thecomponent refrigerant of lower boilingpoint is evaporated in erant ofhigher boiling point is evaporated. In

other words, the various refrigerant componentsevaporate together butthe component of lower boiling point is evaporated in greater amount sothat the first vapor produced is rich inthe component of lower boilingpoint, leaving the liquid weak therein but rich in the component ofhigher boiling point. As the multiple refrigerant continues through theevaporator greater amounts of the component of higher boiling pointevap- The evaporation in greater proportion of the refrigerant of lowerboiling point (the more volatile refrigerant) prevents the refrigerantof higher boiling point from volatilizing prematurely in greatquantities and, accordingly, the temperatures of the medium to be cooledand the refrlgeffective surface of the evaporator throughout its lengthisbeing utilized at relatively high efllciency as compared to a systemutilizing a. single refrigerant which volatilizes substantially atconstant temperature, so that the temperature differential at the bottomof the evaporator where the.

medium to be cooled is introduced, is great and the temperaturedifferential at the top of the evaporator, where the medium to be cooledleaves the-evaporator, is small. In such case where a single refrigerantis used, only a fraction of the surface of the evaporator is operated athigh effleiency and the remainingportion of the surface ofl theevaporator is operated at relatively low emciency.

By utilizing two component refrigerants in sub-- stantial equilibriumbetween the liquid and vapor phases, a better mean effective temperaturedifference is obtained than is otherwise possible, and loss oftemperature head is avoided as in the case where remixing of liquid canoccur.

By utilizing condenser and evaporator surfaces of the same size as thatwhich would ordinarily be used when the system is charged with a singlerefrigerant, the logarithmic mean effective temperature differencebetween the coolant and medium to'be cooled would be the same as for theordinary system, but due to the fact that this temperature differenceremains practically constant for each element of the surface, thearithmetic mean effective temperature difference is decreased andconsequently also the total effective temperature range between coolerand condenser temperatures with a' corresponding decrease in the amountof power required. Alternatively, the amount of surface or the amount ofcoolant could be decreased in comparison with the amounts ordinarilyused and a new balance struck between surface, coolant quantities andpower.

The system in accordance with the invention can be used where coolant isat a premium so that while under ordinary conditions, a system utilizinga single refrigerant could not be operated, a system in accordance withthe instant invention may be operated satisfactorily with less than anormal amount of coolant for the condenser.

Another advantage flowing from the invention is that it enables the useof small self-contained apparatus as for room cooling purposes, wherethe surface for cooling and condensing may be reduced and a minimum ofrefrigerant employed. Such advantages apply not only to unitary apparatus but may be applied generally in a wide variety of applicationswhere the vapor and liquid travel together (of two different butmiscible refrigerants) and are inequilibrium, so that the refrigeranttemperature from beginning to the end of the interchanger can be variedand thus maintain a substantially constant temperature difference incounterflow relationship with the gas or liquid contactingthe surfacethrough which the refrigerants pass.

It will be obvious to those skilled in the art that various changes maybe made without departing from the spirit of the invention and thereforethe invention is not limited to what is shown in the drawings anddescribed in the speciflcation but only as indicated in the appendedclaims.

What is claimed is:

-1. The method of producing refrigeration comprising progressivelyevaporating a plurality of miscible refrigerant components havingdifferent boiling points by passing in generally counterflowrelationship thereto a medium to be cooled, said components havingsuch'varying boiling points and being so proportioned that thetemperature differential between the medium to be cooled flowing in heatexchange relationship with'the refrigerants and the refrigerants issubstantially constant throughout the entire path of heat interchange,compressing the gases formed by the volatilization of the components.

of the multiple refrigerant, condensing the compressed gases, and thenre-evaporating the liquefled multiple refrigerant to repeat therefrigerating cycle.

2. The method of producing refrigeration comprising progressivelyevaporating a plurality of miscible refrigerant components havingdifferent boiling points by passing in generally counterflowrelationship thereto a medium to be cooled, said components having suchvarying boiling points and being so proportioned that the temperaturedifferential between the medium to be cooled flowing in heat exchangerelationship with the refrigerants and the refrigerants is substantiallyconstant throughout the entire path of heat interchange, compressing thegases formed by the volatilization of the components of the multiplerefrigerant, condensing the compressed gases by passing in counterflowrelationship thereto a coolant, the quantities of each refrigerantcomponent within. the condenser being so proportioned and each componenthaving a different condensation point corresponding to differenttemperature-pressure relationships that the temperature differentialbetween the multiple refrigerant and the coolant is substantiallyconstant throughout the path of heat exchange of the' coolant, and thenre-evaporating the liquefied multiple refrigerant to repeat therefrigeration cycle.

3. A method of efficiently utilizing the heat exchange surfaces of arefrigeration system which consists in supplying a mixture of misciblerefrigerant components of different boiling points in gaseous form to acondenser, passing the mixture in the condenser in counterflow relationwith a coolant passing through the condenser to condense a liquid richin the component of higher boiling point, and continuing passage of themixture through the condenser in heat exchange relation with coolant ofprogressively lower temperature to progressively liquefy greater amountsof the component of lower boiling point until all of the component oflower boiling point is liquefied.

4. A method of efficiently utilizing the heat exchange surfaces of arefrigeration system which consists in supplying a mixture of misciblerefrigerant components of difierent boiling points in gaseous form to acondenser, passing the mixture in the condenser in counterflow relationwith a coolant passing through the condenser to condense a liquid richin the component of higher boiling point, and continuing passage ofthemixture through the condenser in heat exchange relation with coolantof progresively lower temperature to' progressively liquefy greateramounts of the component of lower boiling point until all of thecomponent of lower boiling point is liquefied thereby maintaining asubstantially constant temperature difference 9,403,? 7 throughout thecondenser between the coolant and the refrigerant mixture.

5. A method of fllciently utilizing the heat exchange surfaces of arefrigeration system which consists in supplying a mixture oi misciblerefrigerant components of different boiling points in gaseous form toa'condenser, passing the mixture in the condenser in counterflowz.relation with a coolant passing through the condenser to condense aliquid rich in the component of higher boiling point, continuing passage(of the mixture through the condenser in heat exchange relation withcoolant of progressively lower temperature to progressively liquefygreater amounts of the component of lower boiling point until all of thecomponent of lower boiling point is liquefied, then supplying the liquidmixture of miscible refrigerant components of diflerent boiling pointsto an evaporator, progressively evaporating the mixture as it travelsthrough the evaporator with the liquid and vapor phases in substantialequilibrium by passing in generally counterflow relation thereto amedium to be evaporator with the liquid and vapor phases in substantialequilibrium by passing in generally counterflow relation thereto amedium to be cooled thereby forming a vapor rich in the corn- 1 ponentof lower boiling point, continuing pas! sage of the mixture through theevaporator in heat exchange relation with medium to be cooled 'ofprogressively higher temperature until the component of higher boilingpoint is evaporated, compressing the gases formed by the volatilize.-tion of the components of the multiple refrigerant, then supplying themixture of miscible refrigerant components of difi'erent boiling pointsin gaseous form to a condenser, passing the mixture in the condenser incounterflow relation with the coolant passing through the condenser tocondense a liquid rich in the component of cooled thereby forming avapor rich in the component of lower boiling point, and continuingpassage of the mixture through the evaporator in heat exchange relationwith medium to be cooled of progressively higher temperature until thecomponent of higher boiling point is evaporated.

6. A method oi efllciently utilizing the-heat exchange surfaces of arefrigeration system which consists in supplying a liquid mixture ofmiscible refrigerant components of different boiling points to anevaporator, progressively evaporating the mixture as it travels throughthe higher boiling point and continuing passageof the mixture throughthe condenser in heat exchange relatlon with coolant of progressivelylower temperature to progressively liquefy greater amounts of thecomponent of lower boiling point until all of the component of lowerboiling point is liquefied.

CARLYLE M.

REFERENCES CITED The following references are of record int he file ofthis patent:

UNITED STATES PATENTS

